X11: update XDND protocol from version 4 to 5 (#988)

Some applications insist on sending XDND protocol version 5 and
rejected (ignored) FLTK as DND receiver because we allowed only
protocol version 4. Known apps: Google Chrome and Chromium.

This commit enables XDND protocol version 5 in FLTK programs as
DND receiver.

1 files changed, 18 insertions, 13 deletions

diff --git a/src/Fl_x.cxx b/src/Fl_x.cxx
index ede3e1608..9f06c5421 100644
--- a/src/Fl_x.cxx
+++ b/src/Fl_x.cxx
@@ -580,7 +580,6 @@ void open_display_i(Display* d) {
   fl_XdndStatus         = XInternAtom(d, "XdndStatus",          0);
   fl_XdndActionCopy     = XInternAtom(d, "XdndActionCopy",      0);
   fl_XdndFinished       = XInternAtom(d, "XdndFinished",        0);
-  fl_XdndEnter          = XInternAtom(d, "XdndEnter",           0);
   fl_XdndURIList        = XInternAtom(d, "text/uri-list",       0);
   fl_Xatextplainutf     = XInternAtom(d, "text/plain;charset=UTF-8",0);
   fl_Xatextplainutf2    = XInternAtom(d, "text/plain;charset=utf-8",0); // Firefox/Thunderbird needs this - See STR#2930
@@ -1471,13 +1470,19 @@ int fl_handle(const XEvent& thisevent)
     }
     Fl::e_number = old_event;
     // Detect if this paste is due to Xdnd by the property name (I use
-    // XA_SECONDARY for that) and send an XdndFinished message. It is not
-    // clear if this has to be delayed until now or if it can be done
-    // immediately after calling XConvertSelection.
-    if (fl_xevent->xselection.property == XA_SECONDARY &&
-        fl_dnd_source_window) {
-      fl_sendClientMessage(fl_dnd_source_window, fl_XdndFinished,
-                           fl_xevent->xselection.requestor);
+    // XA_SECONDARY for that) and send an XdndFinished message.
+    // This has to be delayed until now rather than sending it immediately
+    // after calling XConvertSelection because we need to send the success
+    // status (retval) and the performed action to the sender - at least
+    // since XDND protocol version 5 (see docs).
+    // [FIXME: is the condition below really correct?]
+
+    if (fl_xevent->xselection.property == XA_SECONDARY && fl_dnd_source_window) {
+      fl_sendClientMessage(fl_dnd_source_window,            // send to window
+                           fl_XdndFinished,                 // XdndFinished message
+                           fl_xevent->xselection.requestor, // data.l[0] target window
+                           retval ? 1 : 0,                  // data.l[1] Bit 0: 1 = success
+                           retval ? fl_dnd_action : None);  // data.l[2] action performed
       fl_dnd_source_window = 0; // don't send a second time
     }
     return 1;
@@ -1591,22 +1596,22 @@ int fl_handle(const XEvent& thisevent)
        - data.l[0] contains the XID of the source window.
        - data.l[1]:
            Bit 0 is set if the source supports more than three data types.
-           The high byte contains the protocol version to use (minimum of the source's and 
+           The high byte contains the protocol version to use (minimum of the source's and
            target's highest supported versions). The rest of the bits are reserved for future use.
        - data.l[2,3,4] contain the first three types that the source supports. Unused slots are set
            to None. The ordering is arbitrary.
-       
+
        If the Source supports more than three data types, bit 0 of data.l[1] is set. This tells the
          Target to check the property XdndTypeList on the Source window for the list of available
          types. This property should contain all the available types.
-       
+
        BUT wayland gnome apps (e.g., gnome-text-editor) set bit 0 of data.l[1]
        even though their source supports 2 data types (UTF8 text + a gnome-specific type)
        and put None (==0) in each of data.l[2,3,4].
        The same gnome apps run in X11 mode (GDK_BACKEND=x11) clear bit 0 of data.l[1]
        and support only UTF8 text announced in data.l[2].
        FLTK wayland apps set bit 0 of data.l[1] and support only UTF8 text.
-       
+
        Overall, the correct procedure is
        if (bit 0 of data.l[1] is set) {
          get the XdndTypeList property
@@ -2686,7 +2691,7 @@ void Fl_X::make_xid(Fl_Window* win, XVisualInfo *visual, Colormap colormap)
     }
 
     // Make it receptive to DnD:
-    long version = 4;
+    Atom version = 5; // max. XDND protocol version we understand
     XChangeProperty(fl_display, xp->xid, fl_XdndAware,
                     XA_ATOM, sizeof(int)*8, 0, (unsigned char*)&version, 1);